This invention relates generally to phase change memory devices.
Phase change memory devices use phase change materials, i.e., materials that may be electrically switched between a generally amorphous and a generally crystalline state, for electronic memory application. One type of memory element utilizes a phase change material that may be, in one application, electrically switched between a structural state of generally amorphous and generally crystalline local order or between different detectable states of local order across the entire spectrum between completely amorphous and completely crystalline states. The state of the phase change materials is also non-volatile in that, when set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until changed by another programming event, as that value represents a phase or physical state of the material (e.g., crystalline or amorphous). The state is unaffected by removing electrical power.
During the fabrication of phase change memories, electrodes within a memory cell may oxidize, leading to significant resistance increases. These increases may result in defective products. The number of cells in memories failing the high resistance tests may be reduced by taking great care in the processing steps and step sequences to minimize any opportunity for oxidation. However, such steps add to the cost of manufacturing the products and may not always be completely effective.
Thus, there is a need for better ways to reduce the resistance increase, product failures, or other adverse consequences of electrode oxidation in phase change memories.